SIMD-0137

TL;DR

Update the curve25519 syscalls functions from returning an error code 1 (`Ok(1)` in rust) to returning an error type `Err(SyscallError::InvalidAttribute)` when invoked on unsupported curve id or group op id. The curve25519 syscall functions should never be invoked on an unsupported curve or operations and such behavior is an unrecoverable program error. Updating the syscall functions to return an error type variant will immediately abort a transaction execution.

Summary

Update the curve25519 syscalls functions from returning an error code 1 (`Ok(1)` in rust) to returning an error type `Err(SyscallError::InvalidAttribute)` when invoked on unsupported curve id or group op id. The curve25519 syscall functions should never be invoked on an unsupported curve or operations and such behavior is an unrecoverable program error. Updating the syscall functions to return an error type variant will immediately abort a transaction execution.

Motivation

There is currently inconsistency between the curve25519 and alt_bn128 syscall functions on unsupported curve inputs. If the curve25519 syscalls are invoked on an unsupported curve or group operation id, the curve25519 syscalls return error code of `1` (`Ok(1)` in rust) while the alt_bn128 syscalls immediately aborts with error code `SyscallError::InvalidAttribute` (`Err(SyscallError::InvalidAttribute`). It would be great to update these functions so that this behavior is handled consistently between the curve syscalls. Since calling these syscalls on an unsupported curve or group op should never be done by a program and is an unrecoverable error, it makes sense to update the curve25519 syscalls to also immediately abort when invoked on an unsupported curve id or ops.

Key Changes

• Curve point validation: on input a curve id and a byte representation of a curve point, verifies whether the input represents a valid curve point.
• Curve point group operations: on input a curve id, operation id, and two byte representations of curve points, either adds, subtracts, or multiplies the input points.
• Curve point multiscalar multiplications: on input a curve id, a vector of scalar, and a vector of curve points, performs a multiscalar multiplication on the input scalars and points.

Impact

Returning an error `Err(...)` on an unsupported curve or operation will prevent a program from mishandling an accidental mis-use of the syscall functions. It will also make the curve25519 and alt_bn128 syscalls for consistent in the way they handle unsupported curves.

Backwards Compatibility

_(Optional)_ The curve25519 syscalls are enabled on testnet and devnet. Therefore, we will need to feature gate the change. Programs using this syscall may need to adapt to the new error handling behavior, but this should not be a big issue since programs should not generally be calling the syscalls on an unsupported curve to begin with.

Security Considerations

A program should never invoke the syscalls on an unsupported curve or operation. If the syscall function returns `Ok(1)` as is currently implemented, it is still possible for the program to handle the error and abort. However, if the syscall function returns an actual error `Err(...)`, then the program will automatically abort execution, removing the possibility that the caller program handles the error incorrectly.